package org.apache.ibatis.ibator.internal.util;

import java.lang.reflect.Array;

/**
 * This class is from javapractices.com:
 * 
 * http://www.javapractices.com/Topic28.cjp
 * 
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 * 
 * Example use case:
 * 
 * <pre>
 * public int hashCode()
 * {
 *     int result = HashCodeUtil.SEED;
 *     // collect the contributions of various fields
 *     result = HashCodeUtil.hash(result, fPrimitive);
 *     result = HashCodeUtil.hash(result, fObject);
 *     result = HashCodeUtil.hash(result, fArray);
 *     return result;
 * }
 * </pre>
 */
public final class HashCodeUtil
{
    /**
     * An initial value for a <code>hashCode</code>, to which is added contributions from fields. Using a non-zero value decreases collisons of
     * <code>hashCode</code> values.
     */
    public static final int SEED = 23;
    
    /**
     * booleans.
     */
    public static int hash(int aSeed, boolean aBoolean)
    {
        return firstTerm(aSeed) + (aBoolean ? 1 : 0);
    }
    
    /**
     * chars.
     */
    public static int hash(int aSeed, char aChar)
    {
        return firstTerm(aSeed) + aChar;
    }
    
    /**
     * ints.
     */
    public static int hash(int aSeed, int aInt)
    {
        /*
         * Implementation Note Note that byte and short are handled by this method, through implicit conversion.
         */
        return firstTerm(aSeed) + aInt;
    }
    
    /**
     * longs.
     */
    public static int hash(int aSeed, long aLong)
    {
        return firstTerm(aSeed) + (int)(aLong ^ (aLong >>> 32));
    }
    
    /**
     * floats.
     */
    public static int hash(int aSeed, float aFloat)
    {
        return hash(aSeed, Float.floatToIntBits(aFloat));
    }
    
    /**
     * doubles.
     */
    public static int hash(int aSeed, double aDouble)
    {
        return hash(aSeed, Double.doubleToLongBits(aDouble));
    }
    
    /**
     * <code>aObject</code> is a possibly-null object field, and possibly an array.
     * 
     * If <code>aObject</code> is an array, then each element may be a primitive or a possibly-null object.
     */
    public static int hash(int aSeed, Object aObject)
    {
        int result = aSeed;
        if (aObject == null)
        {
            result = hash(result, 0);
        }
        else if (!isArray(aObject))
        {
            result = hash(result, aObject.hashCode());
        }
        else
        {
            int length = Array.getLength(aObject);
            for (int idx = 0; idx < length; ++idx)
            {
                Object item = Array.get(aObject, idx);
                // recursive call!
                result = hash(result, item);
            }
        }
        return result;
    }
    
    // / PRIVATE ///
    private static final int fODD_PRIME_NUMBER = 37;
    
    private static int firstTerm(int aSeed)
    {
        return fODD_PRIME_NUMBER * aSeed;
    }
    
    private static boolean isArray(Object aObject)
    {
        return aObject.getClass().isArray();
    }
}
